This invention relates to a resin composition for semiconductor encapsulation not containing metal powder coated with a resin, ultra-fine metal powder, metal powder having low magnetism, etc, and a method and apparatus for producing such a resin composition. The present invention relates also to a resin-sealed semiconductor device using such a resin composition.
Conventional semiconductor devices are fabricated by packaging a semiconductor device onto a lead frame as a substrate and molding other portions with a resin, as is well known in the art. Recent down-sizing electronic appliances has created a demand for a reduction in the size and thickness, and higher performance of, semiconductor devices. Miniaturization of semiconductor devices, for example, has been mainly promoted by improvements in lead frames and molding resins. In line with this trend, a TSOP (Thin Small Outline Package) having a reduced thickness and QFP (Quad Flat Package) to cope with a multi-pin structure have been developed. A ball grid array (BGA) type package and a chip size package (CSP) have been developed to cope with the problems that the package size becomes greater with the increase of the number of pins and handling of package becomes more difficult as the pitch of external leads becomes smaller.
A resin composition, containing an epoxy resin as a main agent and inorganic fillers such as molten silica, has been generally used as a molding resin in the fabrication of the semiconductor devices described above. Such a resin composition is generally produced in the form of powder and particles through a series of unit operations of melt-kneading, pulverization, etc, of the mixture of starting materials such as epoxy resin, a curing agent, an inorganic filler, and so forth. More concretely, the resin composition in the powdery particle form is produced in the following way. The selected starting materials are mixed and the resulting mixture is molten, kneaded and cooled by metallic apparatuses such as a roll, an extruder, a kneader, etc. The mixture is thereafter pulverized by a pulverizing mill, a grinding mill, and so forth. When the powdery particles are produced through such a series of unit operations, however, the problem develops in that conductive metal powder originating from the metal material of the production apparatuses used mixes into the powdery particles.
Even though the mixing amount may be small, the conductive metal powder contained in the sealing resin composition can exert great influences on performance of the resulting semiconductor device. Chip size packages (CSP), for example, are produced by forming Cu bumps for external terminals by plating on a semiconductor wafer, applying resin molding by using a molding resin composition, forming solder balls on the Cu bumps and dicing the resulting processed semiconductor wafer into discrete semiconductor devices. In the resulting package, very fine wires having a wiring width/wiring gap =10 xcexcm/10 xcexcm are applied to the semiconductor wafer, and the thickness of the resin composition layer for molding the spaces between the wires is about 80 to about 120 xcexcm. If any limited voids are contained in the resin composition layer, reliability of the semiconductor devices drops. Moreover, when a conductive metal powder exists in the mixture, the wires are short-circuited and this invites breakage of the device. In the case of a QFP, the gap of wire bonding tends to become smaller with the increase of the number of I/O pins. Therefore, the presence of the conductive metal powder contained in the sealing resin composition, if any, results in a remarkable drop in the reliability of the semiconductor devices.
In the CSP described above and in the QFP having wire bonding of a small pitch, and furthermore, in resin molded semiconductor devices using so-called xe2x80x9clead framexe2x80x9d or xe2x80x9cTAB tapexe2x80x9d, a semiconductor molding resin composition not containing conductive metal powder has therefore been desired to further improve device reliability.
When conductive metal powder is contained in the molding resin composition used for the fabrication of the semiconductor devices, it is a customary practice to insert a magnetic rod into the powder of the resin composition produced, and to stir the powder to remove the metallic powder. Though this method is effective for removing a metal powder having a relatively large size and a ferromagnetic metal powder, it is not sufficient to remove the metal powder having a relatively small particle size or the magnetic powder having relatively low magnetism. It has therefore been desired to efficiently separate and remove not only the metal powder having a large particle size and the ferromagnetic metal powder but also the metal powder having a smaller particle size and the metal powder having low magnetism.
Japanese Unexamined Patent Publication (Kokai) No. 9-173890 discloses a drum type metal classification-recovering apparatus for separating and recovering any foreign metal having magnetic property (iron dust, iron powder, etc) contained as a mixture in the powder of a resin pellet, or the like, although the technology of this reference is not directed particularly to remove the metal powder from the molding resin composition used for the fabrication of the semiconductor devices. The xe2x80x9cPrior Artxe2x80x9d of this Japanese Unexamined Patent Publication (Kokai) No. 9-173890 illustrates a drum type metal classification-recovering apparatus 60 shown in FIG. 1. Reference numeral 61 in FIG. 1 denotes a case, and a cylindrical non-magnetic drum 63 having a built-in semi-circular cylindrical magnetic drum 62 is turnably disposed inside the case 61. Two scrapers 71 are fitted at symmetrical positions on the surface of the non-magnetic drum 63. A hopper 64 for receiving a raw material 65 to be processed, a guide plate 66 for guiding the raw material 65 and a damper 67 for continuously supplying a suitable amount of the raw material 65 to the magnetic drum 62 are provided above the case. A partition member 72 is disposed at the lower part of the case, and a raw material discharge port 69 and a discharge port 73 for foreign metal are provided on both sides of the partition member 72.
FIG. 2 shows a magnetic circuit construction of the non-magnetic drum 63 shown in FIG. 1. A substantially semi-circular magnetic member 74 is fixed to a shaft 78 through an arm 77. Permanent magnets 75 are magnetized in a thickness-wise direction so that the portion thereof on the side of the non-magnetic drum 63 constitutes the N pole. Permanent magnets 76 are magnetized in the thickness-wise direction so that the portion thereof on the side of the non-magnetic drum 63 constitutes the S pole. These permanent magnets 75 and 76 are arranged alternately and equidistantly on the outer peripheral surface of the magnetic member 74 that is made of a steel. Thus, both permanent magnets 75 and 76 constitute a magnetic circuit through the magnetic member 74. In other words, both permanent magnets 75 and 76 constitute a magnetic circuit in which the magnetic flux a flowing out from the N poles of the permanent magnet 75 generates the magnetic field on the surface of the non-magnetic drum 63, permeates through the foreign metal 70 having a magnetic property, magnetically attracts the foreign metal 70 and returns to the S pole of the permanent magnet 76.
In the drum type metal classification-recovering apparatus 60, the main raw material 68, as non-magnetic material inside the raw material 65 that is charged from the hopper 64, is not affected by the magnetic force generated from the magnetic drum 62. Therefore, the raw material 68 falls freely due to its own weight, and is discharged from the raw material discharge port 69. On the other hand, the foreign metal 70 having magnetic property contained as mixture in the raw material 65 are affected by the magnetic force generated from the magnetic drum 62 and are attracted to the surface of the non-magnetic drum 63. When the non-magnetic drum 63 is rotated counter-clockwise RD, the foreign metal 70 is carried into the lower part of the case 61 by the scrapers 71 while they are kept attracted to the surface of the non-magnetic drum 63. After being conveyed to the right-hand region of the partition member 72 in the drawing, the foreign metal 70 is released from the influences of the magnetic force generated from the magnetic drum 62, fall from the surface of the non-magnetic drum 63, is discharged from the discharge port 73 for the foreign metal, and is thus separated from the main raw material 68 and recovered.
As described above, the drum type metal classification-recovering apparatus 60 according to the prior art selects and recovers the main raw material 68 by attracting the foreign metal 70, that is mixed in the raw material 65, by the magnetic force of the magnetic drum 62, and transfer them by the scrapers 71. The drum type metal classification-recovering apparatus of this kind has the magnetic circuit construction shown in FIG. 2. Since the intensity of the magnetic force generated from the magnetic drum 62 is limited, however, classification-recovery efficiency drops remarkably when the magnetic foreign metal is very small particles.
The drum type metal selection-recovery apparatus described in Japanese Unexamined Patent Publication (Kokai) No. 9-173890 solves the problem of the drop of classification-recovering efficiency described above. As shown in FIG. 3, this improved drum type metal classification-recovering apparatus is the same in the basic construction as the drum type metal classification-recovering apparatus shown in FIGS. 1 and 2. However, an improvement can be made in the magnetic drum. In the drum type metal classification-recovering apparatus, a part of which is shown in FIG. 3, a magnetic member shaped into a substantially semi-circular cylindrical shape has the outer peripheral portion that is shaped into a substantially gear-like tooth-shaped sectional shape. In other words, recesses 74a and projections 74b are alternately formed in the circumferential direction. First magnets 79 and 79xe2x80x2, the direction of magnetization of which is substantially the same as the tangential direction of the magnetic drum 62 (magnetized in the width-wise direction of the magnet) are disposed in the recesses 74a of the magnetic member 74. Second magnets 80 and 80xe2x80x2, the direction of magnetization of which is substantially the same as the direction normal to the magnetic drum 62 (magnetized in the thickness-wise direction of the magnet) are disposed at the projections 74b of the magnetic member 74.
The first magnets 79 and 79xe2x80x2 adjacent to each other are disposed so that the magnetic poles having the same polarity oppose each other. In other words, one of the first magnets 79 has the N pole on the side of the second magnet 80, and the other first magnet 79xe2x80x2, too, has the N pole on the side of the second magnet 80.
Furthermore, the second magnets 80 and 80xe2x80x2 are disposed in such a fashion that the magnetic poles on the side closer to the non-magnetic drum 63 have the same polarity as the magnetic poles of the contact surface of the first magnets. In other words, since the magnetic poles of the contact surfaces of the first magnets 79 and 79xe2x80x2 adjacent to each other are S poles, the magnetic pole of the second magnet 80xe2x80x2 on the side of the non-magnetic drum 63 is an S pole.
In the drum type metal classification-recovering apparatus of FIG. 3, due to the specific structure of the magnetic drum as shown in the drawing, the second magnets 80 and 80xe2x80x2 constitute the magnetic circuit by using the projections of the magnetic member 74 (whereby the line of the magnetic flux passes through the projections). Therefore, the effective magnetic path length becomes great, hence the magnet operating point becomes high. In addition, the repulsive force functions between the second magnets 80, 80xe2x80x2 and the first magnets 79, 79xe2x80x2. Consequently, this apparatus can provide a high magnetic force in cooperation with the improvement of the magnet operating point.
FIG. 5 shows a flux density distribution in the circumferential direction on the outer peripheral surface of the non-magnetic drum 63 of the magnetic drum 62 shown in FIG. 3. FIG. 4 shows a flux density distribution in the circumferential direction on the outer peripheral surface of the non-magnetic drum 63 of the magnetic drum 62 shown in FIGS. 1 and 2. To insure the correctness of the comparison, the material, the size, etc, of the magnetic drums of the metal classification-recovering apparatuses are assumed to be common. When the flux density distribution of FIG. 5 is compared with that of FIG. 4 as the prior art, the flux density of FIG. 4 is 285 mT whereas the flux density of FIG. 5 is 433 mT. It can be appreciated that the magnetic drum of FIG. 5 has a high magnetic force about 1.5 times higher than that of the prior art. Therefore, when the drum type metal classification-recovering apparatus of FIG. 3 is employed, it can be expected that magnetic foreign metal, having very fine shapes, mixed in the raw material can be classified and recovered.
However, even in the improved drum type metal classification-recovering apparatus described above, however, the resulting magnetic force is still low. Therefore, this apparatus is not yet sufficient for selectively removing magnetic powder such as metal power coated with a resin, ultra-fine metal powder, metal powder having low magnetism, and so forth, from the molding resin composition used for the fabrication of the semiconductor devices. As a matter of fact, the classification-recovering ratio of the apparatus shown in FIGS. 1 and 2 drops remarkably with the decreasing particle sizes of the magnetic foreign metal because the intensity of the magnetic force generated from the magnetic drum has a limit. In the apparatus shown in FIG. 3, there is a distance between the magnetic drum and the surface of the non-magnetic drum for attracting the magnetic foreign metal. Therefore, the magnetic force generated by the permanent magnets disposed on the magnetic drum does not appear as such on the surface of the non-magnetic drum. Consequently, this apparatus is not suitable for classifying and recovering ultra-fine metal power having sizes (length, diameter, etc) of less than 35 xcexcm, metal powder covered with resin and other metal powders having low magnetism.
It is an object of the present invention to provide an encapsulation resin composition that can solve the problems of the prior art technologies described above, is used particularly for the production of semiconductor devices, and does not contain ultra-fine metal powder having a size of less than 35 xcexcm, metal powder coated with a resin and other metal powder having low magnetism (all of which will be referred thereinafter to xe2x80x9cmagnetic foreign metalxe2x80x9d), in addition to metal powder that can be removed ordinarily by the prior art technologies (hereinafter referred to xe2x80x9cordinary metal powderxe2x80x9d).
It is another object of the present invention to provide a method and apparatus useful for producing the encapsulation resin composition of the present invention and a semiconductor device using the encapsulation resin composition, as will be understood from the following detailed description of the invention.
The above and other objects of the present invention will be understood more fully from the following detailed explanation.
According to one aspect of the present invention, there is provided a semiconductor encapsulating resin composition comprising an epoxy resin, a curing agent and an inorganic filler, wherein the resin composition is powdery particles produced by a series of unit operations including melt-kneading and pulverization of a starting raw material mixture, and wherein foreign metal having magnetic property originating from metal materials constituting a production apparatus used during the unit operations and mixed into the powdery particles is selectively recovered and removed by a drum type metal classification-recovering apparatus.
According to another aspect of the present invention, there is provided a method of producing a semiconductor encapsulating resin composition comprising an epoxy resin, a curing agent and an inorganic filler, comprising processing a raw material mixture of the molding resin composition into powdery particles through a series of unit operations including melt-kneading and pulverization of the raw material mixture; charging the resulting powdery particles into a drum type metal classification-recovering apparatus, and selectively recovering and removing the magnetic foreign metal originating from metal materials constituting a production apparatus used and mixed into the powdery particles.
According to still another aspect of the present invention, there is provided an apparatus for producing a semiconductor encapsulating resin composition comprising an epoxy resin, a curing agent and an inorganic filler, comprising an apparatus for melting and kneading a raw material mixture of the molding resin composition; an apparatus for pulverizing the resulting kneaded matter and forming powdery particles of the molding resin composition; and a drum type metal classification-recovering apparatus for selectively recovering and removing the magnetic foreign metal originating from metal materials constituting an apparatus used for producing the powdery particles of the resin composition, inclusive of the melt-kneading means and the pulverizing means.
According to still another aspect of the present invention, there is provided a resin-sealed semiconductor device produced by encapsulating a semiconductor substrate having bumps for external terminals with a semiconductor encapsulating resin composition while the end face of the bumps are exposed, followed by dicing the semiconductor substrate into discrete devices; wherein the semiconductor encapsulating resin composition is the semiconductor encapsulating resin composition comprising an epoxy resin, a curing agent and an inorganic filler according to the present invention.